1. Field of Invention
The present invention relates to generation of ozone in an electrolytic process using batteries as power source. More particularly, the invention relates to electrolytic generation of ozone using battery and supercapacitor to provide pulse power.
2. Description of Related Art
Among all contaminants in water, the naturally occurring pathogens including enteric bacteria, viruses and protozoan cysts may induce acute illness or even death to users of the contaminated water. In comparison, the malignant effects of other pollutants such as heavy metals are generally non contagious and chronic. Depending on sanitation, water bone diseases caused by pathogenic organisms, for example, Escherichia coli, Salmonella, vibrio cholerae, Rotavirus and Entamoeba histolytica, can easily cause outbreak and become an epidemic. For destroying or screening-out biological contaminants present in a water supply, there are four major disinfection sterilization techniques commonly employed, i.e., chlorination, ozonation, micro or ultra-filtration, and ultraviolet light. In water, ozone is 150 times as powerful as chlorine and 3000 times faster than chlorine on killing microorganism cells. More importantly, ozone leaves only oxygen as residual after it takes a cell membrane apart. The destruction of microorganisms by ozone is more efficient than UV radiation just inhibiting the reproduction of microorganisms by penetrating their genetic materials. Ultra-filtration is expensive on one hand, and it retains microorganisms rather than eliminating the source of evil on the other hand. As a matter of fact, ozone has become the primary disinfectant for municipal water supply around the world.
Ozone is an allotrope of oxygen with three oxygen atoms joined together into a single molecule. Lightening produces ozone naturally by splitting oxygen molecules into single atoms, which combine with oxygen to form the short-lived triangular species. Ozone is also continuously produced in the outer layer of the atmosphere by solar UV radiation. Nevertheless, ozone can be artificially prepared by applying thousands of volts to various number of dielectric tubes comprising of aluminum lined glass tubes to convert air therein into the pungent gas. Many reports using the aforementioned method also known as “corona discharge” have been published, as in U.S. Pat. Nos. 5,503,808, 5,523,310, 5,824,274, and 6,134,806 just to cite a few, as well as numerous commercial ozone generators based on the silent discharge are on the market. Not only a very high voltage is required, but also dry air or pure oxygen is demanded for the corona discharge to generate ozone. As oxygen is split in an electric field of high voltage, so will nitrogen be simultaneously dissociated and hazardous pollutants known as NOx are formed. Removal of humidity from the input air in the discharge ozone generator is to prevent the formation of HNO3 and HNO2 that are corrosive to the generator. Lowering the humidity of the input air for ozone production, which will also lower the dew point of air, is not a small job. Ozone generation can be significantly improved by lowering the dew point, for example, as the dew point is lowered from −40° C. to −50° C. the ozone production efficiency is increased by 15%. However, humidity control is not the only difficulty in ozone production using corona discharge, there are other issues including O3 leakage (harmful to operators and environment), O3 solubility in water, and electrical safety to be taken care as well. Thus, an alternative of ozone generation with high efficiency and less restraint will be beneficial to the general acceptance of ozone for disinfection of microorganisms.
Synthesis of ozone through electrolysis has been known for over 160 years (the first report was by Schonbein; Ann., Vol.50, p.616 (1840)), and the process has been patented over 30 years (for example, U.S. Pat. No. 3,256,164, Jun. 14, 1966). During electrolysis, ozone is formed on the anode of an electrolytic apparatus under the application of a low DC voltage and a high current density. Though the electrolytic process consumes more energy than that of the corona discharge (ca. 6:1), yet it has much higher current efficiency (electrolysis can reach over 50%, while discharge is about 2%), which can well compensate the energy cost. Moreover, the electrolytic process of ozone generation does not have the problems of humidity control, ozone leakage, NOx byproduct, and ozone solubility (ozone has to be dissolved in water for treatment). There are several parameters affecting the yield of electrolytic generation of ozone, they are anode, electrolyte, voltage, current density, and bath temperature. As disclosed in a publication by Foller and Tobias; “The Anodic Evolution of Ozone”;J. Electrochem. Soc., V01.129, No3, Mar. 1982; PP506–515, which is incorporated herein as reference, the ozone current efficiency of over 50% is attained by applying 0.5 A/cm2 to β-PbO2 anode in 7.3M HPF6 aqueous solution at 0° C. Basically, the electrolytic generation of ozone is similar to the electrolysis of water except that a stable material with high oxygen overpotential such as β-PbO2 is used as anode for ozone generation. However, O2 is likewise formed on the anode (the ozone current efficiency is the concentration ratio of O3 to O2) and H2 is formed on the cathode. Many works on electrolytic process of ozone generation dispose an ion-exchange membrane between the electrodes to prevent the mixing of H2 and O2 as they are formed in an electrolysis cell as disclosed in U.S. Pat. Nos. 4,416,747, 4,935,110, 5,114,549, 5,972,196, 5,997,702, and 6,143,163, which are all incorporated herein as reference. A fluorine-containing anion is included in the electrolyte of electrolytic process to improve the yield of ozone generation as in Foller's publication mentioned above and in U.S. Pat. Nos. 4,316,782, 4,541,989 and 5,154,895, the latter is also all incorporated herein as reference. Fluorine-containing anions are generally corrosive and may not be suitable for ozone generation for general use. Since the electrolytic generation of ozone is conducted on low DC voltages and high currents, and provision of the DC power coincides with the characteristics of supercapacitors, the present invention therefore employs a power module comprising batteries and supercapacitors for ozone generation. In addition, the present invention utilizes NaCl for replacing the fluorides as the electrolyte and performs the electrolysis at ambient temperature without a membrane to separate the electrodes. The table salt is a ubiquitous commodity, and the room temperature is easier to maintain than the sub-ambient temperature though the current efficiency of ozone will be somewhat impaired. A simple, affordable, and easy-to-use ozone generator can henceforth be fabricated according to the present invention for the disinfection of water for industries, families, and SPA centers, as well as for surface sterilization of meats, fish, fruits, and for personal hygiene as ozone-containing water may be used for mouth rinsing.